With the constantly improving quality of color photocopies and printings and in an attempt to protect security documents such as banknotes, value documents or cards, transportation tickets or cards, tax banderols, and product labels that have no reproducible effects against counterfeiting, falsifying or illegal reproduction, it has been the conventional practice to incorporate various security means in these documents. Typical examples of security means include security threads, windows, fibers, planchettes, foils, decals, holograms, watermarks, security inks comprising optically variable pigments, magnetic or magnetizable thin-film interference pigments, interference-coated particles, thermochromic pigments, photochromic pigments, luminescent, infrared-absorbing, ultraviolet-absorbing or magnetic compounds.
In addition to static security features used for protecting security documents against counterfeit and illegal reproduction, dynamic security features providing the optical illusion of movement have been developed. In particular, security elements based on oriented magnetic or magnetizable pigments and magnetic or magnetizable optically variable pigments have been developed so as to provide an optical illusion of movement.
WO 2004/007095 A2 discloses the creation of a dynamic optically variable effect known as the “rolling-bar” feature. The “rolling-bar” feature provides the optical illusion of movement to images comprised of oriented magnetic or magnetizable pigments. A printed “rolling bar” type image shows a contrasting band which appears to move (“roll”) as the image is tilted. U.S. Pat. No. 7,517,578 and WO 2012/104098 A1 respectively disclose “double rolling bar” and “triple rolling bar” features, said features seeming to move against each other upon tilting.
WO 2011/092502 A2 discloses moving-ring images displaying an apparently moving ring with changing viewing angle (“rolling ring” effect), said moving-ring images being comprised of oriented magnetic or magnetizable pigments.
Alternatively, methods have been developed to provide security elements displaying a real dynamic motion. US 2012/0074682 discloses a method for creating a visual animation on a medium, the disclosed method include a step of disposing at least two excitable agents on the medium in at least two adjacent respective zones, each of said agents generating a visual effect in response to one and the same stimulus. US 2012/0174447 discloses a security element comprising an optical system that may exhibit a visual animation effect during successive observations by changing the direction of observation of the security element. The disclosed optical system comprises a transparent or translucent substrate, on the side of a first surface of the substrate a combined image comprising a plurality of encoded interleaved images, on the side of second surface of the substrate opposite the first, an exposing screen placed on top of the combined image, which enables the encoded images to be observed during a change in the direction of observing the security element relative to the optical system, wherein the encoded images are observable from the side of the first surface and from the side of the second surface of the substrate.
A need remains for security elements displaying a dynamic visual motion as anti-copy protection means for security documents, said security elements combining an easy detection and recognition while still being difficult to copy.